Android: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo

I am making an android application for generating gr codes and when it is launched, this error occurs. I don't know why this is happening

FATAL EXCEPTION: main
     Process: gq.egor.qrcodegenerator, PID: 26906
     java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{gq.egor.qrcodegenerator/gq.egor.qrcodegenerator.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference

my MainActivity class:

private val imageView: ImageView? = findViewById(R.id.imageView)
private val text = "Hello World!"

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
}

fun generateQR(view: View) {
    val writer = QRCodeWriter()
    val bitMatrix = writer.encode(text, BarcodeFormat.QR_CODE, 512, 512)
    val width = bitMatrix.width
    val height = bitMatrix.height
    val bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.RGB_565)
    for (x in 0 until width) {
        for (y in 0 until height) {
            bitmap.setPixel(x, y, if (bitMatrix.get(x, y)) Color.BLACK else Color.WHITE)
        }
    }
    imageView?.setImageBitmap(bitmap)
}